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• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
  • C07C41/01—Preparation of ethers
  • C07C41/05—Preparation of ethers by addition of compounds to unsaturated compounds
  • C07C41/06—Preparation of ethers by addition of compounds to unsaturated compounds by addition of organic compounds only
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/013—Preparation of halogenated hydrocarbons by addition of halogens
  • C07C17/04—Preparation of halogenated hydrocarbons by addition of halogens to unsaturated halogenated hydrocarbons
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/23—Preparation of halogenated hydrocarbons by dehalogenation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/25—Preparation of halogenated hydrocarbons by splitting-off hydrogen halides from halogenated hydrocarbons
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
  • C07C41/01—Preparation of ethers
  • C07C41/18—Preparation of ethers by reactions not forming ether-oxygen bonds
  • C07C41/24—Preparation of ethers by reactions not forming ether-oxygen bonds by elimination of halogens, e.g. elimination of HCl

Definitions

• the present invention relates to a process for preparing fluorohalogenethers. More specifically the invention relates to fluorohalogenethers which by dehalogenation or dehydrohalogenation allow to obtain perfluorovinylethers. Still more specifically the present invention relates to a process for preparing perfluorovinylethers, preferably perfluoromethylvinylether, perfluoroethylvinylether and perfluoropropylvinylether, with improved yields and selectivity, and using precursors not belonging to the chlorofluorocarbon (CFC) class and besides obtainable without expensive separation processes from hydrogenated by-products.
• CFC chlorofluorocarbon
• perfluorovinylethers are useful monomers for preparing various polymers, from fluorinated elastomers to fluorinated thermoprocessable semicrystalline polymers.
• U.S. Pat. No. 3,817,960 relates to the preparation of perfluorovinylethers of formula: CF 3 O(CF 2 O) n′′ CF 2 CF 2 OCF ⁇ CF 2
• n′′ can range from 1 to 5.
• acylfluoride of formula: CF 3 O(CF 2 O) n′′ CF 2 C(O)F by TFE oxidation at low temperature in the presence of U.V. radiations or by electrochemical fluorination of the corresponding hydrogenated acylfluoride. Then the acylfluoride is reacted according to the following scheme:
• U.S. Pat. No. 3,896,179 relates to the separation of perfluorovinylethers having a linear alkyl chain from branched alkyl chain isomer perfluorovinylethers by thermal decomposition at temperatures in the range 300°-600° C.
• branched isomers generally act as chain transfer agents giving polymers having poor mechanical properties. Therefore branched vinylethers are undesired when linear vinylethers are used for obtaining polymers.
• U.S. Pat. No. 4,340,750 relates to the preparation of perfluorovinylethers of formula: CF 2 ⁇ CFOCF 2 R 0 f X 1 wherein R 0 f is a C 1 -C 20 perfluoroalkyl optionally containing oxygen, X 1 ⁇ H, Cl, Br, F, COOR 0 , CONR 0 R′ wherein R 0 is a C 1 -C 10 alkyl group and R′ represents H or a C 1 -C 10 alkyl group.
• an acylfluoride together with iodine and tetrafluoroethylene is used. In this process the final step of the alkaline acylfluoride pyrolysis is avoided.
• the synthesis scheme is the following:
• the reaction scheme is the following:
• the drawback of this process is that the precursors for obtaining the fluoroepoxides (1a) are industrially hardly available.
• U.S. Pat. No. 5,350,497 relates to the preparation of perfluoroalkylvinylethers through the fluorination with fluorine of partially fluorinated hydrodichloroethers and subsequent dechlorination, according to the following scheme:
• This process has the drawback that the fluorination step with fluorine takes place with not high yields and an excess of fluorine is employed to replace all the hydrogen atoms.
• the fluorination step can be carried out by electrochemical fluorination or by fluorination with fluorine according to U.S. Pat. No. 5,488,142.
• the former reaction generally takes place with low selectivity and formation of undesired by-products.
• industrially acceptable yields and productivity are not obtained.
• the fluorination with fluorine requires long reaction times, necessary for obtaining a complete fluorination of the compound. It is known that the fluorination of hydrogenated compounds is a very exothermic reaction which can cause the breaking of carbon-carbon bonds with formation of undesired by-products.
• EP 1,352,892 describes a process for preparing fluorinated vinylethers from acylfluorides, obtained by decomposition of fluorinated esters.
• the scheme is the following:
• the complete fluorination of the partially hydrogenated precursor esters is achieved obtaining the corresponding perfluorinated esters.
• This step of the complete fluorination of the partially fluorinated ester requires that the reaction is carried out for very long times, with several additions of a hydrogenated compound, for example benzene, to favour the total conversion of the ester. Contemporaneously the reaction temperature must be increased, for example from ⁇ 10° C. up to room temperature. The productivity of this kind of fluorination is very low.
• the synthesis of said olefin is generally carried out by dehalogenation of the tetrachloro difluoroethane CCl 2 FCCl 2 F (CFC 112) with metallic zinc in alcoholic solvent. See for example Houben Weyl, vol. E 10 B2, pages 125-161.
• the CFC 112 precursor used in this synthesis is a chlorofluorocarbon which, as said, falls within the Montreal protocols and its amendments on the reduction of the gas emissions destroying the ozone layer in the stratosphere. According to these protocols the CFC emissions must be gradually reduced in the time until they are then completely eliminated.
• CFC 112 was obtained as a component of a mixture of various chlorofluoroethanes, symmetric and asymmetric, mainly CFC 113 (CF 2 Cl—CFCl 2 ) and CFC 114 (CF 2 Cl—CF 2 Cl).
• CFC 112a brings to the formation of CFC 1112a which, as well known, is a very toxic product. From the industrial point of view, CFC 112a must therefore be reduced to very low values, however, as said, this brings to very high losses in the target product CFC 112.
• the Applicant has surprisingly and unepectedly found a process overcoming the above technical problem.
• the Applicant has surprisingly and unexpectedly found that, with the process of the invention, it is possible to obtain in particular perfluoromethylvinylether, perfluoroethylvinylether in high yields and selectivity. Furthermore in the process of the invention, when the fluorohalogencarbon (III) is a symmetric organic compound, that is Y ⁇ Cl and Y′ ⁇ Y′′, the impurity of the corresponding asymmetric isomer, when present, is in a very reduced amount, lower than 2%, preferably lower than 1%.
• CFC 112 obtained in step 1a) (in formula (III) Y′ ⁇ Cl, Y′′ and Y are both Cl), contains very reduced amounts of the asymmetric isomer 112a (CCl 3 —CClF 2 ), and can be removed by fractional distillation.
• step 1a) the fluorination reaction takes place by addition of gaseous fluorine, optionally in the presence of an inert diluent as, for example, N 2 , He, etc., to the olefins of formula (II), liquid at the reaction temperature.
• an inert diluent as, for example, N 2 , He, etc.
• a solvent or a mixture of inert solvents can optionally be used, in the liquid state and miscible among each other under the conditions in which this step is carried out.
• Step 1a) generally is carried out at temperatures between ⁇ 120° C. and +10° C., preferably ⁇ 90° C. and ⁇ 15° C.
• step 2a) the dehalogenation (chlorine or bromine removal) of fluorohalogencarbons (III) is, for example, carried out by reaction of said compounds with transition metals as zinc, copper, manganese or metal couples as Zn/Cu, Zn/Sn, Zn/Hg, in the presence of solvents as, for example, hydrogenated protics as, for instance, alcohols, or hydrogenated ethers as, for example, glymes, dioxane, or dipolar aprotic solvents such as, for example, DMF, DMSO.
• transition metals as zinc, copper, manganese or metal couples as Zn/Cu, Zn/Sn, Zn/Hg
• solvents as, for example, hydrogenated protics as, for instance, alcohols, or hydrogenated ethers as, for example, glymes, dioxane, or dipolar aprotic solvents such as, for example, DMF, DMSO.
• step 2a) the dehydrohalogenation (HCl or HBr removal) of the fluorohalogencarbons of formula (III) takes place, for example, by reacting these compounds with an inorganic base, preferably NaOH or KOH, or an organic base, preferably primary, secondary or tertiary alkyl or aryl amines. Liquid phase is generally used.
• the elimination reaction of hydrohalogenic acid in step 2a) can optionally be carried out in the presence of a solvent, preferably aqueous or alcoholic.
• the reaction can be carried out in the presence of a quaternary ammonium or phosphonium salt as ammonium or phosphonium tetrabutyl, preferably chloride, ammonium or phosphnium trioctyl benzyl, preferably chloride, etc.
• a quaternary ammonium or phosphonium salt as ammonium or phosphonium tetrabutyl, preferably chloride, ammonium or phosphnium trioctyl benzyl, preferably chloride, etc.
• other salts as, for example, sulphonium salts, can be used.
• dehalogenation or dehydrohalogenation step 2a generally one operates at temperatures in the range 0°-150° C., preferably 25°-100° C.
• the perfluoroalkyl hypofluorites with number of carbon atoms equal to or higher than 2 are known from U.S. Pat. No. 4,827,024.
• the trifluoromethyl hypofluorite is known in the art.
• Step 3a) can be carried out in various ways; for example in the reactor containing the olefin at the liquid state, optionally diluted with an inert solvent under the reaction conditions, the hypofluorite is fed, prepared in liquid or gaseous phase, diluted in a compound inert under the reaction conditions.
• the optional solvents usable in steps 1a) and 3a) are selected from the following: (per)fluoropolyethers, (per)fluoroalkanes, hydrofluorocarbons (HFC), hydrochlorofluorocarbons (HCFC), chlorofluorocarbons (CFC), perfluoroamines, hydrofluoroethers or hydrofluoropolyethers or mixtures thereof.
• the ratio between the reactants in the various steps is not critical.
• step 4a) the dehalogenation or elimination of chlorine or bromine from fluorohalogen ethers of formula (I) is for example carried out by reaction of said compounds with transition metals as zinc, copper, manganese or metal couples as Zn/Cu, Zn/Sn, Zn/Hg, in the presence of solvents which can be either hydrogenated protics as alcohols, or hydrogenated ethers as glymes, dioxane, or dipolar aprotic solvents as DMF, DMSO.
• transition metals as zinc, copper, manganese or metal couples as Zn/Cu, Zn/Sn, Zn/Hg
• solvents which can be either hydrogenated protics as alcohols, or hydrogenated ethers as glymes, dioxane, or dipolar aprotic solvents as DMF, DMSO.
• step 4a) the dehydrohalogenation or elimination of HCl or HBr from the fluorohalogenethers of formula (I) takes place, for example, by reacting these compounds with an inorganic base, preferably NaOH or KOH, or an organic base, preferably primary, secondary or tertiary alkyl or aryl amines.
• an inorganic base preferably NaOH or KOH
• an organic base preferably primary, secondary or tertiary alkyl or aryl amines.
• the elimination reaction of hydrohalogenic acid in step 4a) can optionally be carried out in the presence of a solvent, preferably aqueous or alcoholic.
• the reaction can be carried out in the presence of a quaternary ammonium or phosphonium salt as ammonium or phosphonium tetrabutyl, preferably chloride, ammonium or phosphnium trioctyl benzyl, preferably chloride, etc.
• a quaternary ammonium or phosphonium salt as ammonium or phosphonium tetrabutyl, preferably chloride, ammonium or phosphnium trioctyl benzyl, preferably chloride, etc.
• other salts as, for example, sulphonium salts, can be used.
• dehalogenation or dehydrohalogenation step 4a one generally operates at temperatures in the range 0°-150° C., preferably 25°-100° C.
• the process of the present invention can be carried out in a discontinuous, semicontinuous or continuous way.
• the semicontinuous process can be carried out by feeding gaseous fluorine and the olefin of formula (II) in the reactor containing the solvent or the mixture of the reaction solvents.
• the fluorohalogenethers of formula (I), preparable with the process of the present invention are for example the following: CF 3 O—CFCl—CF 2 Cl, C 2 F 5 O—CFCl—CF 2 Cl, C 3 F 7 O—CFCl—CF 2 Cl, CF 3 O—CFH—CF 2 Cl, C 2 F 5 O—CFH—CF 2 Cl, C 3 F 7 O—CFH—CF 2 Cl.
• perfluoroalkyl hypofluorites and chlorinated and chlorofluorinated olefins are used, wherein in particular chlorofluorinated olefins have high purity and thus contain remarkably reduced amounts of toxic impurities.
• the starting olefin is CFC 1112
• the amount of CFC 1112a is very low, for example lower than 2% by weight, preferably lower than 1% by weight. Therefore the process of the invention allows to produce CFC 112 containing very low amounts of CFC 112a, so as to obtain the olefin CFC 1112 in high purity and reduced amounts of CFC 1112a.
• 10 l/h of gaseous fluorine, 5 l/h of CO and 10 l/h of nitrogen are contemeporaneously allowed to flow in an AISI 316 steel pipe (inner diameter 2.17 mm and length 100 mm).
• the reaction is triggered by heating the gas mixing zone at 100° C. for some minutes.
• the reactor is cooled by air circulation so that the temperture is lower than 300° C.; at the reactor outlet the temperature is 250° C. Under these conditions CO and F 2 are converted into COF 2 with a yield higher than 95% (determined by IR analysis of the outflowing gaseous mixture).
• the gaseous mixture after cooling at 100° C., is allowed to flow through a catalytic bed formed of 300 g of fine milled anhydrous CsF having particle size lower than or equal to 0.1 mm, mixed with 300 g of needle-shaped copper having diameter of 0.2 mm and length 6-7 mm.
• the catalyst is placed in a tubular reactor (inner diameter 55 mm, length 250 mm).
• the reaction temperature among gases is maintained at 100° C. Under these conditions the COF 2 is converted into CF 3 OF with yield higher than 98%, determined by IR analysis of the outflowing mixture.
• a solution formed of 25.5 g of trichloroethylene (TCE) and 475 g of CF 3 O—CFCl—CF 2 Cl as reaction solvent is introduced into a 400 cc AISI 316 reactor, equipped with mechanical stirrer.
• the solution is cooled, by a cryostat, at the temperature of ⁇ 70° C. and under stirring one mole of fluorine diluted with nitrogen in a molar ratio 1/2 is fed through a bubbling inlet. Contemporaneously 1.07 moles of TCE are fed by a pump. The reactants are fed in 8 hours, maintaining the tem-perature at ⁇ 70° C.
• the reaction is carried out for 3 hours and the final solution analyzed by GC/MS.
• the PCE conversion is quantitative.
• the selectivity, expressed in % by moles, in CCl 2 F—CCl 2 F (CFC 112) is 81%.
• the CFC 112a is present in the reaction mixture in a reduced amount (0.5% with respect to the CFC 112).
• hypofluorite CF 3 —CF 2 —CF 2 OF is synthesized according to the Example 8 of U.S. Pat. No. 4,827,024.
• Example 2 In the reactor used in the Example 1 and maintained at the temperature of ⁇ 90° C., wherein 121.2 g of CFCl ⁇ CFCl (CFC 1112), obtained as from Example 2, and 452 g of CF 2 Cl —CF 3 (CFC 115) as reaction solvent were previously introduced, 2.3 Nl/h of hypofluorite are fed. The reaction lasts 4 hours and the final solution is analyzed by GC/MS.
• the selectivity in propyl adduct CF 3 —CF 2 —CF 2 O—CFCl—CF 2 Cl, referred to the fed hypofluorite, is 48.1%.
• hypofluorite CF 3 —CF 2 OF is synthesized according to the Example 1 of U.S. Pat. No. 4,827,024.
• the selectivity in ethyl adduct CF 3 —CF 2 O—CFCl—CF 2 Cl, referred to the fed hypofluorite, is 79%.

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